This invention relates to an improved glass panelled fireplace screen and more particularly to a screen which seals the fireplace opening to impede the passage of air so as to reduce very substantially the loss of warm room air up the chimney when the fireplace is not in use.
It is well known that most fireplaces have poorly closing dampers which provide little or no sealing effect. As a result, significant volumes of heated room air pass out of the house by way of the chimney when the fireplace is not in use. Typically, even under conditions of moderate outdoor wind velocity, it is not unusual for heated room air to escape via the fireplace chimney at a rate of 200 cubic feet per minute. For example, if the outside air temperature is 32.degree. F. and the inside room temperature is 72.degree. F., the escaping flow of room air carrier energy from the house at a rate in excess of 200,000 BTU per day. In a typical home having a furnace rated at 100,000 BTU/hr this energy loss must be made up by the furnace having to run more than two extra hours per day. The chimney loss becomes much worse during colder weather and/or when the wind velocity is high.
The marketplace provides glass panelled fireplace screens as means to reduce this loss of energy from the house. Conventional screens, however, do not seal a fireplace very efficiently. Such glass-panelled fireplace screens generally comprise a rectangular framed structure containing four panels of tempered, heat resistant glass which are hinged together in folding pairs, such that each bi-folding pair opens outwardly to provide access to one half of the fireplace opening. Because these so-called bi-fold screens are mass produced to sell at reasonable, competitive prices, the clearances between the panels and their frame structure must be large enough to take into account the substantial buildup of manufacturing tolerances in all their separate parts. As a consequence, even the best screens on the mass market have such wide gaps around the panels, when they are closed, that they provide only a 30% to 40% reduction in the wasteful loss of room air via the chimney.
A further problem with conventional fireplace screens lies in the primitiveness of their manual draft control mechanisms. Such screens generally utilize manually operated draft controls comprising a perforated, slideably moveable plate mounted within the bottom cross member of the frame, behind a stationary perforated plate. When the perforations of the two plates are in registry, the draft control is open permitting air to flow through to ventilate the fire. When the sliding plate is moved so that the perforations of the two plates are out of registry, the draft control is closed. In such condition the draft control is intended to prevent the loss of room air via the chimney, after the fire is out. Such draft controls have two inherent disadvantages: (1) the thin sheet metal sliding plates are guided only at their ends and do not lie flat against the stationary plate so that even when they are closed, these draft controls leak, and, (2) someone must remember to manually close the draft control.